Two men responsible for Thursday's firebomb attack in the West Bank were found among 12 men arrested overnight near Kalkilya, according to an Israeli security official.
The two are subject to investigation by the Israel Security Agency, the Shin Bet.
One of the men is suspected to be responsible for throwing the firebomb, the other of assisting him.
A firebomb was thrown at a private vehicle in the West Bank on Thursday near Ma'ale Shomron, leaving 11-year-old Ayala Shapira severely burned and her father more lightly injured.
The girl suffered third-degree burns over 30-40 percent of her body when the car was set ablaze and remains in serious condition, as doctors continue fighting to save her life.
Though her situation slightly improved overnight, she is still in serious condition, according to the Sheba Medical Center at Tel Hashomer, the hospital where she is anesthetized.
The incident occurred east of Kalkilya in the West Bank, where the IDF launched a widescale search for the attackers and where an overnight raid led to the arrests of the 12 Palestinians.
Prime Minister Benjamin Netanyahu spoke to Yossi Dagan, the acting head of the Samaria Regional Council, following Thursday evening's incident. "Tell the family we stand by their side and wish them a fast recovery," Netanyahu said.
Dagan briefed the premier on the happenings of Thursday's incident, telling him of the terror-filled reality that Samaria residents deal with on a daily basis, with the constant threat of stone throwing and fire bombs.
He asked Netanyahu to react to the attack by strengthening the settlement movement. "The most appropriate response to terror of this kind against innocent civilians is strengthening Jewish settlement," Dagan said.
Terror in Samaria must be addressed by building, developing, and expanding Jewish settlement in the region, he added.
"We will lay our hands on the perpetrators of this terror attack," said Defense Minister Moshe Ya'alon at Ma'ale Shomron, where he was updated by security officials on the situation, "and we will reach their dispatchers."
The response to the attack was swift, Ya'alon said, praising the IDF and Israel's Security Agency, the Shin Bet, for "knowing how to effectively respond to terrorism" and deploying quickly to the scene as events were unfolding.
Fighting these types of attacks is complicated and requires determination and the use of force – "something Israel is doing now and will continue to do."
The defense minister visited Ayala at the Sheba Medical Center where he encouraged her family to "be strong," assuring the worried parents that she is "in good hands."
These acts of terror, he said at the hospital, are meant to instill fear in the residents of Judea and Samaria. "But from my many conversations with them, it is clear they will not be deterred."